The present invention relates to a paper-making method in which pulp is suspended in water, and water is removed from the obtained pulp suspension in order to form a fiber web or a fiber sheet. The present invention relates in particular to a paper-making method in which water is removed from a pulp suspension which contains an organic polymer and an inorganic oligomer.
In addition, the present invention relates to an aqueous pulp suspension intended for use in the above-mentioned paper-making method or a bonding agent composition to be added to the circulating water of the paper-making process, containing an organic polymer and an inorganic oligomer or a compound which in an aqueous solution hydrolyses to an oligomer.
There are previously known paper-making methods in which water is removed from a pulp suspension which contains as the organic polymer a cationic or amphoteric guar gum or a cationic starch, and as the inorganic oligomer a colloidal silicic acid. In these prior known paper-making methods the ratio of the guar gum to the silicic acid, calculated as SiO.sub.2, has been 0.01-25:1 and the ratio of the cation-active starch to the silicic acid has been 1-25:1.
The above-mentioned prior known bonding agent systems are, however, relatively expensive, and they are strongly dependent on the pH. It has been shown experimentally that their action decreases considerably when the pH drops below six. These prior known bonding agent systems also do not yield a good result when paper is made from pulps which contain groundwood.
The object of the present invention is therefore to provide a paper-making method and a bonding agent combination intended for use in the method, a combination by means of which it is possible to make paper having properties at least as good as those obtained by using the above-mentioned prior known bonding agent systems, and the action of which is not dependent on fluctuations of the pH in the process, or on whether the paper is made using neutral sizing or under acid conditions. A further object of the present invention is to provide a paper-making method and a bonding agent system intended for use in the method, by means of which it is possible to make paper from all kinds of pulp, such as groundwood pulp, bleached or unbleached cellulose, filler-free or filler-containing pulp, and by using the method and the bonding agent system according to the invention it is thus possible to make newsprint, SC-quality paper, fine paper, cardboard, liner, bag paper, etc.
The object of the present invention is, furthermore, to provide a bonding agent combination in which the inorganic oligomer, or the compound forming the oligomer, is a product having an economical price.